The present invention relates generally to equipment utilized and operations performed in conjunction with wireless telemetry and, in an embodiment described herein, more particularly provides a shear coupled acoustic telemetry system for use with a subterranean well.
Typical acoustic telemetry systems used in subterranean wells include at least one stack of piezoceramic elements, or other electromagnetically active elements (piezoelectrics, magnetostrictives, electrostrictives, voice coil, etc.) to generate axial stress waves in a wall of a tubular string. This due to the fact that it is generally considered that axial stress waves are less attenuated as compared to other types of stress waves (torsional, flexural, surface, etc.) in a tubular string positioned in a wellbore environment.
Thus, past acoustic telemetry systems have tended to use transmitters which are axially inline with the tubular string wall for most efficient axial coupling between the transmitter and the wall. To maximize the volume of the electromagnetically active elements, the transmitter is usually positioned in an annular cavity internal to the tubular string wall, with annular-shaped elements axially inline with the wall and concentric with the tubular string.
However, such configurations pose certain problems. For example, tubular strings used in wellbores typically have very limited thickness in their walls, providing only limited available volume for acoustic transmitters. As another example, each different size of tubular string requires that a different-sized transmitter be designed specifically for that tubular string, which eliminates any possibility of interchangeability between transmitters and tubular strings. Furthermore, axially coupled transmitters are not well suited for taking advantage of other modes of transmission (such as flexural, torsional, shear, etc.) or multi-mode combinations, which may be more advantageous for short distance acoustic transmission.